Surface functionalization of Si6Li6 cluster with superalkalis to achieve high nonlinear optical response: A DFT study

Abstract

In this study, the nonlinear optical (NLO) response of pure and superalkali (Li3O, Na3O, and K3O) doped Si6Li6 clusters has been explored. The doping of superalkalis on the Si6Li6 cluster significantly narrowed the wide HOMO-LUMO energy gap (5.27 eV) of the pure Si6Li6 cluster up to 3.83 eV. All superalkali doped clusters reveal electride nature based on the HOMOs’ electron density. The thermodynamic stability of these electrides is anticipated through their interaction energies with the highest value (3.90 eV) for Si6Li6-Li3O. The NLO properties of superalkali doped Si6Li6 electrides are investigated through first and second-order hyperpolarizabilities. These complexes exhibit large first hyperpolarizabilities as compared to pristine Si6Li6. Among superalkali doped clusters, Si6Li6-K3O showed the highest first hyperpolarizability of 1.42 × 104 au. The small crucial excitation energies are responsible for such a high NLO response. For dynamic NLO response, electro-optic Pockel’s effect and second harmonic generation are calculated. A very large quadratic NLO response (3.61 ×10−9 au) is observed for the Si6Li6-Li3O complex. The quantum theory of atoms in molecules (QTAIM) analysis shows the electrostatic interaction between interacting species. All the electrides exhibit ultrahigh transparency in the UV–VISIBLE region. These intriguing results are self-serving to promote promising applications of Si6Li6-based clusters in high-performance nonlinear optical materials.